- discord: large_image as <art_base_url><lower titleId>.png when
configured (Discord accepts external URLs in asset fields);
uploaded-asset keys remain as fallback via application_id
- cfg: art_base_url field with load/save support
- scripts/sync_icons.sh: FTP pulls all icon0.png (read-only)
- deploy/ARTWORK.md rewritten around URL-pack-first design
